Automatic Identification of Screen Ruling on Printed Copy
Publication Date: 2003-Jan-30
The IP.com Prior Art Database
When processing images which need to be descreened it is necessary to select the screen ruling of the origination before the scan as this determines the scan resolution and enables optimum screen filtering to be used. This requires the user to know what the screen resolution is of the origination. Most users can not tell what the screen resolution is simply by looking at the origination and require the aide of a manual tool to determine the screen. This in itself can be difficult to use and can be a time consuming process to conduct (ie. Find the manual tool, select a suitable area, twist the tool to give the desired result). It is possible to measure the screen ruling by analysing a high resolution scan of a small area of the image. Thus the screen ruling can be determined automatically without user intervention. This process consists of 1. Automatically identifying a suitable region for close examination from a low resolution preview that has not been descreened 2. Scanning the suitable region at a high enough resolution not to alias the screen and calculate the screen ruling from the Fourier transform.